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shaggybaxter said..
I am utterly fascinated with windvanes. A non electrical powered auto helm that's reliable and efficient enough to put other energy in-energy out devices to shame.
Dumb question from an ignoramus...is there any dampening effect on the rudder movement as boat speed increases?
On my autohelm, there is a damping effect as the boat accelerates. At low speed, the rudder movement is large in comparison to high speeds where the rudder movement tapers off. This is because the higher the speed, the less rudder input is required. It's linear, so the amount of input is variable right across the speed range.
Does a Fleming work like this? I understand how they work, but not the fine detail.
Thanks!
SB
Edit: If I understand what Gary is referencing, a variable sheeting position increases/decreases the reaction time, but not the amount of throw, is that right?
Windvane steerings biggest downfall is with boats that accelerate fast like yours and catamarans. The relative wind change as boats jump onto the plane does not suit a vane.
Windvanes with bevel gears have an automatic feedback where as the Z crank types need some experimental feed back work. The windblade itself on modern windvane is on an axis that is canted back at about 15 degrees. They are often referred to as horizontal servo windvanes but the axis is actually at between 15 and 20 degrees depending on the brand.
When the blade is on a horizontal axis the blade will generate the same power all the way over to 45 degrees either side of the vertical position. This is undesirable and causes over steering. With about 15 degrees axis the blade develops less power as it reaches 45 degrees of deflection. With bevel gears the oar is being altered immediately the blade leans over and the boat is being brought back on course. When the boat is travelling at about 5 knots the angle applied to the oar is probably only a couple of degrees, this is all it takes to force the oar over and correct the tiller. Watching the oar in a breeze the movement is hardly noticeable. Not sure if the system would suit boats doing 15 to 18 knots.
As a side note I was at Bunnings in Warrawong the other day. They have poly carbonate 8mm sheets there. Same stuff Monitor and Fleming etc use for blades. $21 sheet would be enough for 3 blades.